The present invention relates to conducting communications over packet-switched networks such as Internet Protocol (IP) networks. More particularly, the present invention relates to conducting mobile communications over IP networks.
Voice or telephony services can now be provided over packet-switched networks, such as the Internet. These packet-switched networks are commonly referred to as IP networks, IP telephony networks or Voice over IP (VoIP) networks because the Internet Protocol according to various IP based standards is the primary protocol used. One such IP based standard, for example, is the International Telecommunication Union (ITU) H.323 Standard.
The H.323 Standard provides a foundation for audio, video, and data communications across IP networks. By complying with the H.323 Standard, multimedia products and applications from multiple vendors can interoperate, allowing users to communication without concern for compatibility. The H.323 Standard is part of a larger series of communications standards that enable audio video conferencing across a range of networks.
The H.323 Standard defines four major components for network based communications, namely, terminals, Gateways (GW) Gatekeepers (GK) and Multipoint Control Units (MCU).
Terminals are the client endpoints on the network that provide realtime two-way communications. All terminals which comply with the H.323 standard must also support the ITU H.245 Standard, which is used to negotiate channel usage and capabilities. Further, terminals which comply with the H.323 standard are required to implement the ITU Q.931 and the H.225 standards for call signaling and call setup, including for example, Registration/Admission/Status (RAS) processing. Optional capabilities in terminals which comply with the H.323 standard are MCU capabilities.
A gateway is an optional element when implementing the H.323 standard. Each gateway provides many services the most common being a translation function between the H.323 standard conferencing endpoints and other terminal types. Each gatekeeper acts as a central point for all calls or communications within a zone serviced by the gatekeeper and provides call communication control services to registered endpoints. The gatekeeper could be considered a virtual switch. The MCU supports conferences between three or more endpoints.
Each of the above described endpoints, GW, GK, and MCU can be implemented by use of apparatus such as a personal computer (PC), workstation, server, etc.
The above described H.323 standard as defined is intended to operate in fixed packet-switched networks where the endpoints, for example, terminals such as workstations, PC""s, etc., that conform to the H.323 standard, do not move to a new zone serviced by another gatekeeper. Further, packet-switched networks defined according to the above described H.323 standard are not intended to accommodate the communications (i.e., message signaling) between a Mobile Station (MS) and a Mobile Services Switching Center (MSC). Such message signaling is defined according to e.g., the GSM or the Code Division Multiple Access (CDMA) standards.
In a typical mobile system (e.g., GSM), the signaling between each MS and the MSC is based on circuit switched connectivity, (e.g., in GSM system Signaling Connection Control Part (SCCP)/Link Access Protocol on the D-Channel (LAPD)/Link Access Protocol on the Dm-Channel Message (LAPDm) connectivity that is achieved by using dedicated timeslots in A- and Abis-interfaces). Since a timeslot based circuit switched connectivity model is used, there usually is not any addressing information present in signaling messages. The timeslot itself, is sufficient for addressing the circuit switched connection to the MS. Also, whenever there are more than one simultaneous logical signaling connection between the MSC and one MS, all of these logical connection transactions use the same circuit switched connection for signaling needs. The different logical connections are distinguished by Protocol Discriminator and Transaction Identifier (TI) parameters. For call control purposes the two first parameters are always the same, but the TI distinguishes between two (or more) logical call control sessions. Such as, for example, where one call is active and another is on hold. It should be noted that each TI must be unique for the MS.
IP telephony networks, on the other hand, do not rely on timeslot-based circuit switched connectivity. In H.323 based telephony networks the signaling is done using H.225.0 standard call control messages that provide logical call identifier and are transmitted over Internet Protocol (IP) connections. An IP telephony network may prefer a centralized signaling model, in which signaling messages, between endpoints A and B are routed through the logical switch (e.g., GK or Call Processing Server (CPS)). For Example, each connection between endpoints A and B according to the Q.931 standard includes A-GK and GK-B legs. Each connection is distinguished by a Call Identifier (ID). The same Call ID is used for both legs of the end-to-end connection.
Since in a mobility aware IP telephony network it is possible that one transaction is external (controlled the by MSC) and another internal (controlled by the GK), there is a strong possibility that TIs used for these transactions may clash. This can occur due to the fact that the MSC is not aware of the internal call transactions. An external call is one that is signaled through the network gateway (NW-GW) and possibly controlled by an external switch such as the MSC. An internal call on the other hand is one that is signaled entirely within the IP telephony network or a sub-network thereof (except with respect to the radio interface) and is controlled by the logical switch of the sub-network such as the GK.
Two alternatives have been proposed to solve the above noted problems.
The first alternative provides only one IP telephony call control connection per active MS and then tunnels simultaneous mobile (cellular) call control messages inside that same IP telephony call control connection. Thus, mapping is performed only between mobile identity which corresponds to circuit switched connectivity, and the IP telephony call control connection. Such is performed without taking the TI into consideration, except for performing TI reallocation when TI clashes occurs.
The second alternative provides for the opening of one xe2x80x9crawxe2x80x9d IP connection per active MS and then tunneling all IP telephony call control messages through the one xe2x80x9crawxe2x80x9d IP connection.
The above described first alternative has one clear benefit, in that handover is easier since only one IP telephony call control connection needs to be re-routed. However, a disadvantage of the first alternative is that support of supplementary services is virtually impossible. Since the same Call ID namely, the same IP telephony call control connection, is used for all calls per MS, then it would be very hard to make call transfers for any individual call. Also, the first alternative may easily lead to situations where the Call ID isn""t end-to-end anymore. Namely, the Network Gatway (NW-GW)-GK leg and GK-Radio Access Gateway (RA-GW) leg of the same call may have different Call ID""s. This increases the complexity of the GK.
The second alternative has some advantages, the handover is easier since only one IP telephony call control connection needs to be re-routed. The second alternative also allows for supplementary services support. However, neither alternative is H.323 standard compliant and therefore they do not suit well to an IP telephony network.
To solve the above mentioned TI clashes between internal and external calls, the above described alternatives propose that the GK change the TI value of the external call in such a way that the MSC notices no change. Namely, towards the MSC the GK uses the TI value allocated by the MSC and towards the MS the GK uses some other TI value such as 2.
The above solution however has one major disadvantage. Since the MSC and the MS are not aware of the change of the TI value in the GK, the handover from the IP telephony network to an external network cannot be performed. This is because after the handover, the TI translation functionality of the GK would be removed from the connection thus leaving the MSC and the MS using different TI values for the same transaction. These handovers can only be performed for external call transactions, since the internal call transactions are not known to the MSC. However, these kinds of handovers are possible after the internal call has been released. It should be noted that handovers out of the IP telephony network, while an internal call is happening, is not possible anyway.
Thus, a solution is required for mapping IP telephony call control signaling connections (and Call IDs) to timeslots and TIs of the mobile (cellular) network signaling connections. Particularly, a solution is required which permits more than one transaction (sessions) to be conducted for each MS.
The present invention provides a method and apparatus that permits mobile communications to be conducted over packet-switched networks. Specifically, the present invention provides a method and apparatus for accommodating signaling between a MS and a MSC over an IP network where a new IP telephony signaling connection (e.g., Q931 connection in case of H.323 system) is opened for each transaction.
Specifically, the method and apparatus of the present invention permits mobile communications between a Mobile Switching Center (MSC) and a Mobile Station (MS) and between MSs by establishing for each transaction including a call on an Internet Protocol (IP) connection in an IP network. It should be noted that the present invention is not limited to cases where the first transaction is a mobile terminated external call. Other types of transactions being the first transaction can initiate the procedures of the present invention. The mobile terminated call as the first transaction as described below is, for example, purposes only.
Thus, for example, in the invention a call to a MS is initiated by sending from the MSC to the MS, via the IP network, a (call initiation e.g., paging) message causing the MS to send a response message to the MSC. The response message includes a mobile identity which identifies the MS. Responsive to the response message, the MSC sends to the MS a call set up message that triggers establishment of an IP connection in the IP network upon which a transaction including the call is to be conducted. The call set up message includes a transaction ID which identifies the transaction. The IP network stores the transaction ID from the call setup message, and maps the transaction ID with respect to the mobile identity and the IP connection to be established. The IP connection is established in the IP network according to data stored and mapped in the IP network, thereby permitting mobile communications between the MSC and the MS over the IP network. Another call to the MS from another MS while the previous call is active is handled by establishing another IP telephony signaling connection in the IP network for the other call and mapping a different value for the transaction ID for the other call with respect to the mobile identity of the other MS and a second leg of the other IP connection to be established between said IP network and the MS in a manner to avoid clashes with the previously mapped transaction ID.
With respect to mobile (cellular) systems, the present invention provides for mapping circuit switched connections (e.g., SCCP and LAPD in GSM system) and TI to IP telephony signaling connections (Call IDs). In the present invention, the GK is responsible for solving TI clashes by he reallocating new TIs for those that would otherwise clash with existing ones.
In mobile (cellular) systems, the MS is not usually addressed due to the circuit switched nature of the signaling connection. Therefore, in order to address the MS with an IP telephony signaling message the present invention provides a method and apparatus using a mobile identity (e.g., in GSM, the Temporary Mobile Subscriber Identification/International Mobile Subscriber Identification (TMSI/IMSI), or International Mobile Equipment Identification (IMEI) in case of emergency calls initiated from a MS that has no Subscriber Identity Module (SIM)), as a session ID that uniquely addresses the MS.
Alternatively to the procedure of the present invention described above, where a new IP telephony signaling connection is opened for each transaction, the present invention also provides a procedure where only one Q931 signaling connection is established for each active MS regardless of the number of non-idle call control transactions the MS is involved in.
Further, the present invention provides a procedure where the GK allocates TI values using the highest unused value.